A “roofing underlayment” is a waterproofing membrane having a continuous waterproofing adhesive membrane layer supported on a carrier sheet that may be constructed of nonwoven felt or plastic film.
The membrane adhesive is attached to a roof deck before installation of an overlayment that may consist of roofing tiles, shingles, slate tiles, metal sheeting, or the like. The function of the membrane is to seal around roofing fasteners and to protect against damage from ice dams and wind-driven rain. Roofing underlayments are commercially available from Grace Construction Products, Cambridge, Mass., under the well-known trademark ICE & WATER SHIELD®. Numerous other manufacturers also provide roofing membranes under different tradenames, typically of the plastic carrier sheet variety.
Roofing underlayments having plastic carrier sheets are sometimes coated on the back with a slip resistant material such as sand. Such “granular” underlayments were disclosed, for example, in Zickell et al. U.S. Pat. No. 4,992,315 (See also, Mandzu World Patent International Appl. No. PCT/HUO1/00034; International Publication No. WO 01/73242 Al). Granular membranes are sometimes disadvantageous for the reason that their granular surface interferes with the formation of water-tight laps at seams with other membranes. An applicator attempts to form a seam by overlapping one membrane adhesive onto the back (or upper major face) of an abutting membrane. Consequently, the ability to maintain lap integrity is attenuated unless the sand is removed to expose the upper edge of the abutting membrane to permit direct contact with an overlapped adhesive layer.
Roofing underlayments are commercially available having a slip-resistant continuous coating. Roofing underlayments sold under the ICE & WATER SHIELD® brand by Grace Construction Products, Massachusetts, have a waffle design slip-resistant coating that is applied by slot die and then embossed using an embossing roller. This continuous slip-resistant coating provides applicators with the ability to make strong lap seams.
Other continuous coating designs are known. For example, Thessen disclosed in U.S. Pat. No. 4,897,293 a procedure for coating roofing membranes using linear low-ensity polyethylene (LLDPE) adhesive to create a roughened or texturized surface for skid resistance. The LLDPE adhesive is applied at the nip of two calender rolls, whereby one of the rolls is heated above the melting point of the LLDPE and is rotated a relatively low speed, while the other roll is heated to a temperature below the melting point of the LLDPE, and rotated a greater speed than the first roll. The membrane produced by this method is said to have one smooth surface and an opposite surface having a roughened texture.
In U.S. Pat. No. 5,687,517, Wiercinski et al. disclosed a method for making a roofing underlayment having corrugations due to the use of different plastic film layers in the carrier sheet, and coating the sheet using a polymer coating having a lower Young's modulus of elasticity than the outermost of the film layers. The corrugations provide additional surface area to minimize slippage of boots.
In U.S. Pat. No. 6,296,912, Zickell disclosed a roofing membrane having an asphalt-coated woven or nonwoven layer, disposed against the upper surface of the roofing membrane, to minimize slippage.
Against this prior art background, the present inventors believe that a novel underlayment and method are needed by which skid resistance is imparted in an economic and convenient manner.